Class MethodHandleProxies
- Since:
- 1.7
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Method Summary
Modifier and TypeMethodDescriptionstatic <T> T
asInterfaceInstance
(Class<T> intfc, MethodHandle target) Produces an instance of the given single-method interface which redirects its calls to the given method handle.static boolean
Determines if the given object was produced by a call toasInterfaceInstance
.static MethodHandle
Produces or recovers a target method handle which is behaviorally equivalent to the unique method of this wrapper instance.static Class
<?> Recovers the unique single-method interface type for which this wrapper instance was created.
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Method Details
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asInterfaceInstance
Produces an instance of the given single-method interface which redirects its calls to the given method handle.A single-method interface is an interface which declares a uniquely named method. When determining the uniquely named method of a single-method interface, the public
Object
methods (toString
,equals
,hashCode
) are disregarded as are any default (non-abstract) methods. For example,Comparator
is a single-method interface, even though it re-declares theObject.equals
method and also declares default methods, such asComparator.reverse
.The interface must be public, not hidden, and not sealed. No additional access checks are performed.
The resulting instance of the required type will respond to invocation of the type's uniquely named method by calling the given target on the incoming arguments, and returning or throwing whatever the target returns or throws. The invocation will be as if by
target.invoke
. The target's type will be checked before the instance is created, as if by a call toasType
, which may result in aWrongMethodTypeException
.The uniquely named method is allowed to be multiply declared, with distinct type descriptors. (E.g., it can be overloaded, or can possess bridge methods.) All such declarations are connected directly to the target method handle. Argument and return types are adjusted by
asType
for each individual declaration.The wrapper instance will implement the requested interface and its super-types, but no other single-method interfaces. This means that the instance will not unexpectedly pass an
instanceof
test for any unrequested type.Implementation Note: Therefore, each instance must implement a unique single-method interface. Implementations may not bundle together multiple single-method interfaces onto single implementation classes in the style of
AWTEventMulticaster
.The method handle may throw an undeclared exception, which means any checked exception (or other checked throwable) not declared by the requested type's single abstract method. If this happens, the throwable will be wrapped in an instance of
UndeclaredThrowableException
and thrown in that wrapped form.Like
Integer.valueOf
,asInterfaceInstance
is a factory method whose results are defined by their behavior. It is not guaranteed to return a new instance for every call.Because of the possibility of bridge methods and other corner cases, the interface may also have several abstract methods with the same name but having distinct descriptors (types of returns and parameters). In this case, all the methods are bound in common to the one given target. The type check and effective
asType
conversion is applied to each method type descriptor, and all abstract methods are bound to the target in common. Beyond this type check, no further checks are made to determine that the abstract methods are related in any way.Future versions of this API may accept additional types, such as abstract classes with single abstract methods. Future versions of this API may also equip wrapper instances with one or more additional public "marker" interfaces.
- Type Parameters:
T
- the desired type of the wrapper, a single-method interface- Parameters:
intfc
- a class object representingT
target
- the method handle to invoke from the wrapper- Returns:
- a correctly-typed wrapper for the given target
- Throws:
NullPointerException
- if either argument is nullIllegalArgumentException
- if theintfc
is not a valid argument to this methodWrongMethodTypeException
- if the target cannot be converted to the type required by the requested interface
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isWrapperInstance
Determines if the given object was produced by a call toasInterfaceInstance
.- Parameters:
x
- any reference- Returns:
- true if the reference is not null and points to an object produced by
asInterfaceInstance
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wrapperInstanceTarget
Produces or recovers a target method handle which is behaviorally equivalent to the unique method of this wrapper instance. The objectx
must have been produced by a call toasInterfaceInstance
. This requirement may be tested viaisWrapperInstance
.- Parameters:
x
- any reference- Returns:
- a method handle implementing the unique method
- Throws:
IllegalArgumentException
- if the reference x is not to a wrapper instance
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wrapperInstanceType
Recovers the unique single-method interface type for which this wrapper instance was created. The objectx
must have been produced by a call toasInterfaceInstance
. This requirement may be tested viaisWrapperInstance
.- Parameters:
x
- any reference- Returns:
- the single-method interface type for which the wrapper was created
- Throws:
IllegalArgumentException
- if the reference x is not to a wrapper instance
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